This invention relates to printers and, in particular, to means for masking the inked printing ribbon from the printing surface.
The prior art teaches using a pair of fork-like brackets, one on either side of the printing wires of a wire matrix dot print head, to position or guide the printing ribbon as it passes between the printing surface and the printing styli. The longitudinal travel of each printing stylus, or wire is a very short distance requiring the ends of the printing wires to be placed in close proximity to the printing surface (usually, paper entrained over a platen or roller). Accordingly, an inked printing ribbon positioned between the ends of the printing wires and the printing surface is positioned in a very narrow opening, and this typically results in brushing contact between the printing ribbon and the printing surface. Such contact produces ink smears on the printing surface and an undesirable finished appearance, and it also may add undesirable friction loading on the ribbon and its drive mechanism.
Additionally, snagging or even wedging may occur between the printing ribbon and the printing surface. This is particularly true during vertical feed of the paper. For example, when either the top edge of the paper or horizontal perforations or folds in the paper move vertically past the ribbon, the printing ribbon and the paper may catch one another, thereby very adversely affecting operation of the printing machine. For example, the ribbon is likely to be moved out of its proper position, causing loss of printing even though the print styli strike the paper; further, sheets of paper may become wrinkled or torn and have to be replaced, and the printing ribbon may have to be rethreaded or replaced. Not only does this cause material loss, but even more importantly, loss of time and delay in printing. Such a drawback is particularly significant, and all the more likely to occur, when the printer is designed for high speed printing. These are some of the drawbacks this invention overcomes.